Found a few miscellaneous issues with controller support, and due to a bug report discovered an unusual issue.
Steam and Unreal perform startup on any VR device currently connected, if the VR plugin is installed within the game package (which it is so by default, even if it is never used). Nonetheless, as VR is not a part of Apollyon, I have removed said plugin and solved the issue.
On that note, those new and old to Apollyon are encouraged to report bugs to the developer here on the Steam community, or on the Apollyon discord. Replies and hotfixes will be coming within a few hours on weekdays, in this case!
Now then, have fun meeting only the darkest of spirits!